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Author Topic: Terrorizing family with RFI.  (Read 6079 times)
KK7S
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Posts: 7




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« on: September 11, 2009, 11:19:41 PM »

I'm not sure this is the right forum, but...

I'm running a pretty modest station.  Generally under 100 watts (and typically 10-20).  I'm using 100 ft of RG213 as my feed line up to an HF6V vertical on the roof.  The antennna is at about 30 ft give or take.  It has the Butternet tuned radial kit -- 4 tuned radials.  It also has 4 additional radials for 30 meters. I have a decent RF ground (a pair of 8 ft ground rods) within 10 ft of my rig.  I mostly use CW.  

This setup is causing all kinds of crazy RFI within my house, and my wife is ready to throw my rig out the window.  Any help would be appreciated!

Here are some of the problems I've seen:

- When running at as low as 10 watts (with an IC703), a subwoofer was loudly broadcasting all of my transmissions in our family room.  I wrapped the subwoofer's feed cable around a big ferrite core, and this cut the noise down by about a factor of 10, but the noise is still audible (and is worse with higher power transmission).

- Also at 10 watts, a mouse on a Macintosh in the house audibly clicks whenever I send CW, and even sends some commands to the computer.  I had to disable the "squeeze" gesture on this mouse so that it would stop squeezing every time I transmitted.

- At more than 20 watts output (using a K3), X10 lights in various locations in the house turn on.  

- At more than 50 watts output, the carbon monoxide detector goes off.  It's extremely loud and makes my 6 year old daughter cry hysterically.

It seems to me that I'm using a pretty conservative setup.  In theory, there shouldn't be all that much radiation coming straight down into the house.  

I'm thinking that either A) I've misunderstood how a ground plane antenna works (and a lot more radiation comes straight down than I thought) or B) the feed line is radiating more than I thought it would (due to the fact that the feed line and antenna have greater than 1.5:1 SWR on most operating frequencies, regardless of the fact that I have an ATU at the transmitter and good transmitter/feed-line SWR).  

If (A) is the case then I might just be out of luck, because I don't have many options for other antennas in my current house.  If (B) is the case, then I'm happy to just install a remote antenna tuner at the base of the antenna to ensure that the SWR on the feedline is 1:1.  

Can anyone provide some guidance on this?  Is there some other option that I'm missing?  Anything else I should be considering or testing?  Is there no hope for operating at > 10 watts?  

Thanks,
-Chadd
 AE7CC
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K1CJS
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Posts: 6283




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« Reply #1 on: September 12, 2009, 06:51:05 AM »

Suspect the feedline, the antenna and its connections.  It sounds like the RF power is being 'reflected' back along your feedline and is getting into your house wiring that way.

How good is the 213 cable?  Is it a quality brand--or is it unbranded?  Are the connectors on the cable attached well, clean, (no corrosion) and watertight?  Does the cable ring out (no resistance or opens) end to end on both the center and the shield, and are you sure the cable isn't shorted?

If all these things are OK, the antenna could be the cause.  A poor connection on the antenna may have gotten worse, or a mistake may have been made while assembling the antenna.  Has the RFI always been this bad, or has it just started?

Are the grounds for your antenna and the house electrical grounds connected together?  There may be a potential difference between the two if not--and that will play all kinds of havoc--given the right circumstances.

There are a lot of things to check--even though you may believe the cable and antenna are OK.

Good luck!
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AA4PB
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« Reply #2 on: September 12, 2009, 08:00:19 AM »

First, a single ground rod connected to the radio with a 10-foot long wire doesn't make a good RF ground, but then no RF ground on the radio should be needed.

One issue might be that the antenna and radials are so close to the house. If those radials are on or close to the roof then they could be radiating energy into the house wiring which may not be very far away. Moving the antenna farther away from the house is probably the best solution. Maybe put it on the ground with burried radials out in the back yard or raise the whole antenna/radial system up on a mast to get it farther from the roof.
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Bob  AA4PB
Garrisonville, VA
AA4PB
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« Reply #3 on: September 12, 2009, 08:08:40 AM »

SWR on the feed line doesn't have anything to do with it radiating. An insufficient number of radials (or improperly tuned radials) is what permits RF currents to flow on the outside of the coax shield.

Make sure you have at least 3-4 radials cut to 1/4 wavelength long for each band that you operate. Make sure that the radials are insulated from everything except the grounding point at the base of the vertical. Remember, the radials (especially the far ends) are "hot" with RF. Also the radials can be detuned if they are placed too close to conductive material like gutters, flashing, etc.
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Bob  AA4PB
Garrisonville, VA
KK7S
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Posts: 7




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« Reply #4 on: September 12, 2009, 02:45:35 PM »

Regarding radials:  I have 4 tuned, multi-band radials (from Butternut).  In addition, I have 4 radials cut specifically for 30m.  The radials are lying on (but insulated from) the roof.

Regarding feedline:  It's Belden RG-213/u.  A bit less than 100 ft of it.  

Regarding ground:  I should have said "station ground" or something innocuous like that instead of saying "RF ground".  I have two, 8 ft ground rods, spaced about 10 feet apart, very close to my station.  The ground rods are connected together with 2 AWG stranded copper wire.  They are also connected back to the house electrical ground rod by a LONG run of 2 AWG stranded wire.  The electrical ground is on the opposite end of the house.

I have also been grounding the bulkhead where my coax comes into the house.  I have a couple of SO-239 connectors on a copper bar in a junction box on the outside of the house, and this is where the antenna feedline is connected.  (There is a short run of coax from that bulkhead to my transmitter on the inside of the house.) The copper bar is also connected to ground.  Now this morning, for lack of anything bertter to do, I tried removing the ground from the this copper bar / bulkhead.  This STOPPED the CO detector from going off when I transmit at 100 w.  So that's some progress!  Any thoughts on this development?  Unfortunately, it didn't fix the interference with X10 lights in the house.  

I'm a little confused by the whole issue of exactly where and when to ground and there is a lot of conflicting information about it out there.  I guess I'll raise that topic in the elmers forum.
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WB2WIK
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« Reply #5 on: September 12, 2009, 09:08:47 PM »

I have a similar vertical directly above the house on a Glenn Martin Engineering roof tower, with radials under it, and when running 1500W output power on any HF band, it causes zero interference to anything in the house.  This is only a single story house, so the antenna is right over our heads.

You have something wrong with the installation.

I'd suspect bad coax (open outer conductor connection) or the radials are not really bonded to the outer conductor of the coax at the feedpoint of the antenna...or something like that.

It's impossible to cause all that interference with lower power and a roof mounted vertical, this is pretty much unheard of unless something is simply "wrong" with the installation.

An RF ground on the station equipment should not be required, at all.

WB2WIK/6
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WB5JEO
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« Reply #6 on: September 12, 2009, 09:10:23 PM »

I have a notion of something you might try. These things can be tricky and may be the result of a complex situation. I don't pretend to diagnose from a distance or even to correctly guess the solution. But it's what I'd try, if I had the problem.

Ground systems can, in some circumstances, cause an array of problems, especially when a ground lead is a quarter wave length of an operating frequency. One approach is to disconnect all ground leads at every point, including the house ground rod end. Disconnect the transceiver from all other equipment, except the feedline (disconnecting all coax grounding at the station end). Just radio and feedline to antenna. See if the problem persists.

I don't care if the feedline is radiating or not or if the antenna is resonant or your radials are tuned (they're detuned that close to the roof, anyway, but that's another thread). RF does not reflect back down the feedline and get past the tuner or tuned output circuit. You're not running that kind of power, and you shouldn't be getting RF into the house wiring without some help, most likely from the ground setup or the wiring itself. Folks run all manner of stations with more power than yours and all sorts of strange antennas, including some that wouldn't work at all if the feedline was doing the majority of the radiating without that array of RFI problems. Suspect something that you don't have in common with those stations.

Start hooking back up the station ground, one unit at a time. Just one at a time, or you may miss the point at which a ground loop appears. I suspect you'll get your radio and all local equipment back on the station single point ground and hooked to the station ground rod without the RF problem appearing. If it appears when you hook up the ground lead to the house ground, you may have found the problem (hopefully that simple) and can RF-isolate the ground lead. (Or leave it off, since neither the house ground rod nor the two station ground rods are functional grounds for lightning protection, which means your ground lead from the radio case may do more harm than good.) If it appears earlier, you'll have to do some more hunting. If you have the problems with only the basic radio-feedline-antenna combination, with ground leads off, consider some resonant wiring run in the house, possibly in the attic or upper floor with a roof-mounted antenna. Some experimentation with breakers may help narrow things down.
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WB4BYQ
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« Reply #7 on: September 13, 2009, 04:17:33 AM »

take the grounds off.  test each band for rfi to your equipment.  the radials are the effective ground.  i have seen ground cables of any lenght detune a ant system.  i use a butternet hf6v in the backyard mounted on a angle iron stand that is 4' by 4' with a center pipe about 2.5 feet long welded in the center with cross members and supported from the corners with
iron rods, looks like a pyramid, with 7 radials coming from the base of the vertical, 3 radials 33 feet long, 4 radials 14 feet long.  no ground rod on either the vertical or station.  try each band to see what is the effect, do test the swr, try to get the lowest reading, use a mfj analyzer if you can to see what the ant is doing in ref to the band in tuning.

this problem can be solved.
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AA4PB
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« Reply #8 on: September 13, 2009, 05:21:24 PM »

If this is the Butternut Stub Tuned Radial (STR) system I wonder if the fact they are laying on the roof may be detuning them and making them ineffective. This would be most critical near the ends of the radials. I notice that the STR instructions advise not to let the radials come too close to other objects, especially metal and not to let them hang down onto the roof.
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Bob  AA4PB
Garrisonville, VA
N5LRZ
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Posts: 0




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« Reply #9 on: September 14, 2009, 10:07:00 AM »

There is your possible answer right in your post ...

"I'm using 100 ft of RG213 as my feed line up to an HF6V vertical on the roof."

You may be getting RF directly into the electrical system of your house due the very close proximity of the antenna and its ground field.

Run a little test to find out if this is the case.  Make yourself a little dipole--nothing meant for permanent use/just throw something together.  put it out away from the house and transmit.  IF the interference you stated stops then you know its antenna proximity problems.  Just move the antenna away from the house.
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W6OP
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Posts: 352




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« Reply #10 on: September 14, 2009, 04:19:08 PM »

Some articles of interest to read that may help are;
http://audiosystemsgroup.com/RFI-Ham.pdf
and
http://www.audiosystemsgroup.com/NCDXACoaxChokesPPT.pdf

Pete W6OP
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KH6AQ
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Posts: 7887




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« Reply #11 on: September 14, 2009, 06:36:41 PM »

In the far-field the magnetic fields from the radials cancel and there is no radiation. In the near-field (directly under the radials) there is considerable electric field coupling from the radials to the earth and the house wiring. This causes displacement current. The current will tend to return to the source - in this case the feedpoint of the ground plane antenna.

The solution to reduce the RF current thru the house? Place a number of ferrite beads over the coax at the feedpoint. For a simple installation use a dozen clamp-on ferrite cores. DX Engineering stocks these.
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KH6AQ
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« Reply #12 on: September 15, 2009, 06:08:23 AM »

I ran a quick analysis of something approximating your setup. A 7 MHz quarter wavelength monopole having four resonant radials. The base is 20' above ground.

To reduce feedline shield current by 10 dB requires ferrite beads having an impedance of 1400 ohms. 10 dB may allow you to raise your TX power 10X above the level at which you presently have no RFI symptoms.

Another solution, although it might be a one-band solution is coiled coax balun. For 7 MHz take 30' of Mini-8 coax and wind it into a close-wound coil having a diameter of 6 inches.
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KK7S
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« Reply #13 on: September 15, 2009, 09:32:55 PM »

Thanks for the concrete suggestions.  I'm happy to try these.  

I just want to ensure I understand the theory behind this.  I think you're saying that, for various reasons, power is being reflected back down the shield of the feedline.  I further assume that the feedline shield is radiating this reflected power and causing the bulk of the RFI.  Hence, putting a choke on the feedline might fix the problem.  Have I got this right?
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KK7S
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« Reply #14 on: September 15, 2009, 11:21:51 PM »

Thanks W6OP for the pointer to K9YC's article.  That's a great resource.
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